This invention generally relates to methods and apparatus for measuring the propagation delay of a telecommunications network. More particularly, this invention relates to non-interfering methods and apparatus for measuring propagation delay between communicating devices by using the edge of the data communications passband for sending and receiving signals meant for the measurement of propagation delay.
Data communication between two points theoretically can be conducted at the speed of light. However, due to delays inherent in the communicating devices themselves as well as delays in the intermediate transmitting stations, telecommunications are slowed down. Also, because of the ability of the telephone companies to route communications in many different ways due to local or regional congestion, communication between two points may take a roundabout route. Roundabout routes, however, offer inferior performances compared to more direct routes because of both increased noise and the delay itself. Thus, a good measurement of propagation delay could be beneficial in determining the source of inferior performance.
Presently, techniques for measuring propagation delay of communications between two devices connected by a transmission line require that the data communications on the line be interrupted so that a test of the line can be carried out. Because of the inconvenience of such interruptions, propagation delay is rarely measured.